This invention relates to an improved apparatus for the stability control of a cutter of a nut former. A driving roller placed on the center line of the cutter axis operates in the same direction as the cutter. A pin spindle, slide block and a compressed rod inhibit the cutter from rolling and obtain a uniformity in shearing section of the cutter material. A plate spring and a compressed helical spring are used so that the cutter can avoid chattering (i.e. vibrations and accelerations of the tool) and advance smoothly. For a given same displacement of the cutter, the displacement of the compressed spring is less in compression. As a result, a smaller helical spring may be used and less wear among contacting and sliding surfaces occurs resulting in greater longevity of the apparatus.
The conventional control mechanism of a cutter used in a nut former is disclosed in FIG. 1. The movement of cam 11 causes cam follower and roller 12 to move along a guide slot 111 which in turn urges cutter 13 forward. By means of compressed helical spring 14, the cutter 13 is urged in the direction of Arrow A. Thus cam follower 12 is always urged against the inside surface of guide slot 111 of cam 11. This is to avoid chattering, vibrating or accelleration of cutter at the time of cutting. However, cam 12 is situated below cutter 13 and has a certain clearance (that is to say, moment arm). From a dynamics point of view, cam follower 12 which is driven by a perpendicular component of force to drive the cutter 13 forward must have a horizontal component of force in parallel with cam 11. The horizontal component of force applied on cam 12 and the moment arm form a moment of force and cause the cutter 13 to tend to about its axis. The resulting inability to obtain uniformity of shearing surface of material molding and punch as tends to cause damaging during molding and punch operations. In addition, the yield of defective products increases, thereby hurting production efficiency. For the purpose of reducing the rolling of cutter 13 which is unavoidable, and avoiding chattering at the time of cutting material, a longer compressed helical spring with larger diameter could be used. Practically speaking, the function of compressed helical spring is to reduce the rolling of the cutter and the chattering at the moment of cutting. And the maximum horizontal force applied on the cam 12 takes place within the cutting distance of material by a cutter. From experience and experiment, cutting of material occurs when a cutter cuts into three-tenths of the diameter of a material. In other words, the force of spring reaches maximum when three-tenths of material diamer has been cut be for obtaining the advantage of reducing the rotation of cutter and chattering. But the spring force of the conventional cutter reaches maximum when cutting process nears the end, that is to say, F=KX. As a result, when roller, pin spindle and sliding plate in contact with each sliding surface advance material through the cutter, the force of the spring 14 increases uselessly, thereby increasing the rate of wear and shortening their life. It also causes waste of power.